Dr. Stephen Barrett writes that colloidal silver should not be taken to treat any illness. He says that there have not been any studies done that show that colloidal silver treats illness in vivo. However, he does give a few examples of where colloidal silver was shown to kill germs in vitro.

In another article in the LA Times, a doctor is quoted saying that colloidal silver has been shown to kill germs in vitro, but has not been shown to effectively cure illness.

Stephen Barrett calls colloidal silver "Risk Without Benefit". Stating that it is very well possible that colloidal silver may be entirely ineffective in treating illness even though it has been shown to kill germs in vitro in some tests.

Of course, the fact that a product inhibits bacteria in a laboratory culture doesn't mean it is effective (or safe) in the human body. In fact, products that kill bacteria in the laboratory would be more likely to cause argyria because they contain more silver ions that are free to deposit in the user's skin.

I am skeptical that further tests are needed to confirm that the substance is effective.

Was ever a substance shown to kill germs in vitro, then tested and shown not to be effective in curing illness?

  • 7
    You are implying that all type of illness are caused by bacteria, which is not true, so a substance with no anti-bacterial properties can indeed treat an illness. That said, there are a huge amount of molecules that work in vitro but not in vivo, or work in lab animals but not in humans. Most of the chemicals that are tested in pharmaceutical industries never make it to clinic because of that.
    – nico
    Dec 13, 2011 at 3:52
  • 5
    Well, things that kill germs in vitro but also kill the patient probably aren't seen as "cure"ing anything... Dec 13, 2011 at 5:24
  • 4
    Some examples are hydlochloric, nitric and sulfuric acids.
    – Zano
    Dec 13, 2011 at 7:15
  • When big pharma puts a drug into a clinical trial they usually do so because the substance showed a positive effect in vitro. According to the Tufts Center For Drug Development the total success rate of this process is around 16%. If you consider that pharma companies only focus on making studies on substances that they believe to have a chance to be effective drugs, the true number is probably even lower than 16%.
    – Christian
    Dec 13, 2011 at 11:00
  • 1
    @dmckee chemotherapy for cancer depends on killing the tumor before killing the patient, so substances that can kill the patient are indeed seen as potential cures if administered carefully.
    – jwenting
    Dec 21, 2011 at 6:31

1 Answer 1


Wikipedia is your friend! we have 3 classes of substances that kill bacteria:


Disinfectants are substances that are applied to non-living objects to destroy microorganisms that are living on the objects.

Most disinfectants are also antiseptics.


Antiseptics (from Greek ἀντί - anti, '"against" + σηπτικός - sēptikos, "putrefactive") are antimicrobial substances that are applied to living tissue/skin to reduce the possibility of infection, sepsis, or putrefaction.

Some common antiseptics

The following are all examples of substances that should be used only externally (e.g. on skin but not ingested!)

  • Alcohols
  • Quaternary ammonium compounds
  • Boric acid
  • Brilliant Green
  • Chlorhexidine Gluconate
  • Hydrogen peroxide
  • Iodine
  • Mercurochrome
  • Manuka Honey
  • Octenidine dihydrochloride
  • Phenol (carbolic acid) compounds
  • 4-hydroxybenzenesulfonate (Dibromol).
  • Sodium chloride
  • Sodium hypochlorite
  • Calcium hypochlorite
  • Sodium bicarbonate (NaHCO3)
  • Terpenes
  • Microcyn


An antibacterial is a compound or substance that kills or slows down the growth of bacteria. The term is often used synonymously with the term antibiotic(s).

In order for a substance to be called an antibiotic, in-vivo experimentation must be performed, to determine:

  • Safety (drinking hydrogen peroxide is not a good idea)
  • Efficacy (drinking alcohol will not make you healthier)
  • Minimum effective dosage

The successful outcome of antimicrobial therapy with antibacterial compounds depends on several factors. These include host defense mechanisms, the location of infection, and the pharmacokinetic and pharmacodynamic properties of the antibacterial. A bactericidal activity of antibacterials may depend on the bacterial growth phase, and it often requires ongoing metabolic activity and division of bacterial cells. These findings are based on laboratory studies, and in clinical settings have also been shown to eliminate bacterial infection.

Since the activity of antibacterials depends frequently on its concentration, in vitro characterization of antibacterial activity commonly includes the determination of the minimum inhibitory concentration and minimum bactericidal concentration of an antibacterial. To predict clinical outcome, the antimicrobial activity of an antibacterial is usually combined with its pharmacokinetic profile, and several pharmacological parameters are used as markers of drug efficacy.


Silver is not even known to be an effective antiseptic, let alone an antibiotic. The Cochrane Collaboration, which is the most trusted agent that reviews, collates and meta-analyses medical experiments, has tackled the existing experimental evidence regarding silver, finding no proof that it works:

Wound dressings and creams containing silver are widely used. It is thought that silver may help wounds to heal faster and prevent infection, but we did not know if this was true. This review identified 26 trials (involving 2066 participants) comparing silver-containing dressings or creams against dressings or creams that did not contain silver. Twenty of the trials were on burn wounds, while the other trials were on a mixture of wound types. Most studies were small and of poor quality. After examining them all, the authors concluded that there is not enough evidence to support the use of silver-containing dressings or creams, as generally these treatments did not promote wound healing or prevent wound infections. Some evidence from a number of small, poor-quality studies suggested that one silver-containing compound (silver sulphadiazine) has no effect on infection, and actually slows down healing in patients with partial-thickness burns.

source (emphasis mine).

  • +1: So then, the short answer is "Yes". Thank you. Dec 13, 2011 at 15:40
  • The Cochrane collaboration result is for a very narrow application of silver: in wound dressings. It doesn't count as a general proof that silver isn't an in vitro antibiotic (for which there is some evidence), but it may reinforce the general point that activity in vitro doesn't translate into activity in vivo.
    – matt_black
    Dec 16, 2011 at 0:07
  • @matt_black there is no such thing as an "in-vitro antibiotic"!? Antibiotics work in-vivo (which is what distinguishes them from antiseptics).
    – Sklivvz
    Dec 16, 2011 at 0:17
  • @Sklivvz perhaps my terminology is slightly dodgy, but I intended to argue that silver has known anti-bacterial properties in vitro putting it the antiseptic group by your definition. However, I'm not sure that is quite right as I don't think the group of "all things that kill bacteria" is a perfect match for antiseptics which I tend to think implies some external clinical use making it much more restrictive.
    – matt_black
    Dec 16, 2011 at 11:51

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .